Visible light and base promoted O-H insertion/cyclization of para-quinone methides with aryl diazoacetates: An approach to 2,3-dihydrobenzofuran derivatives

Article abstract of DOI:10.1016/j.cclet.2021.03.010

A visible light and base promoted O-H insertion/cyclization of para-quinone methides with aryl diazoacetates is developed. This one-pot two step reaction offers a mild and efficient approach for the synthesis of biologically important 2,3-dihydrobenzofuran derivatives in good yields and moderate diastereoselectivities.

Full text of DOI:10.1016/j.cclet.2021.03.010

G Model
CCLET-6206; No. of Pages 5
Chinese Chemical Letters xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Communication
Visible light and base promoted O-H insertion/cyclization of
para-quinone methides with aryl diazoacetates: An approach to
2,3-dihydrobenzofuran derivatives
a,b,c,
Shuangjing Zhoua, Baogui Caia, Chuxia Hua, Xu Chenga, Lei Lia, , Jun Xuan
*
*
a
Anhui Province Key Laboratory of Chemistry for Inorganic/Organic Hybrid Functionalized Materials, College of Chemistry & Chemical Engineering, Anhui
University, Hefei 230601, China
Key Laboratory of Structure and Functional Regulation of Hybrid Materials (Anhui University), Ministry of Education, Hefei 230601, China
b
c
Key Laboratory of Precise Synthesis of Functional Molecules of Zhejiang Province, School of Science, Westlake University, Hangzhou 310024, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A visible light and base promoted O-H insertion/cyclization of para-quinone methides with aryl
diazoacetates is developed. This one-pot two step reaction offers a mild and efficient approach for the
synthesis of biologically important 2,3-dihydrobenzofuran derivatives in good yields and moderate
diastereoselectivities.
© 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
Received 30 December 2020
Received in revised form 1 March 2021
Accepted 3 March 2021
Available online xxx
Keywords:
Carbene
2,3-Dihydrobenzofuran
Visible light
para-Quinone methides
Aryl diazoacetates
2,3-Dihydrobenzofuran is one of the most important oxygen-
containing heterocycles, which can be frequently found in various
natural isolates and synthetic bioactive molecules [1]. As some
selected examples shown in Fig. 1, Abiesinol E was isolated from
the bark of Abies sachalinensis with remarkable anti-tumor
activities [2a]. Other 2,3-dihydrobenzofuran containing structures,
such as (+)-Obtusafuran exhibits anticarcinogenic and antifeedant
activities [2b], and Pterocarpan is found to show impressive
antiproliferative activities [2c]. Due to their broad spectra of
pharmaceutical applications, a great deal of efforts has been
devoted to the development of efficient methods towards the
synthesis of 2,3-dihydrobenzofurans over the past several years
[3]. Among the reactions reported, [4 + 1] cycloaddition of para-
quinone methides (p-QMs) [4] with a suitable C1 building block
has been witness as a reliable method for the construction of 2,3-
dihydrobenzofurans. In 2018, Yuan et al. disclosed a catalyst-free
synthesis of 2,3-dihydrobenzofuran derivatives via [4 + 1] cyclo-
addition of p-QMs with sulfur ylides [5]. Shortly after this
discovery, other commonly used C1 synthons, such as sulfonium
salts [6], ammonium bromides [7] and α-halogenated carbonyl
compounds [8] were sequentially investigated to conduct such
valuable cycloaddition reactions. In addition, Waser group
demonstrated a [4 + 1] cycloaddition of para-quinone methides
with allenoates as C1 cycloaddition partner by using commercially
available chiral phosphine as catalyst [9]. Despite these elegant
progresses, further exploring of other C1 units for the synthesis of
biologically important 2,3-dihydrobenzofurans is still appealing
and highly desirable.
Visible light-promoted chemical transformation has attracted
much attentions in the past decade not only because it utilizes
visible-light or direct sun-light as green and sustainable energy
source, but also due to the fact that it can create unique reaction
manifolds in synthetic organic chemistry which are generally
difficult or unavailable to realize under traditional thermal
conditions [10]. Pioneering works disclosed by the group of
Jurberg and Davies [11], He and Zhou [12] revealed that aryl
diazoacetates could efficiently undergo photolysis to generate free
carbene species under blue LED irradiation. Compared with
classical transition metal-catalyzed carbene formation by using
α-diazocarbonyl compounds as carbene precursors [13], these
photochemical processes could be achieved without the need of
exogenous metal catalysts under very mild reaction conditions
[14]. The formed free carbene species has been successfully applied
to the synthesis of various useful products through X-H insertion
* Corresponding authors at: Anhui Province Key Laboratory of Chemistry for
Inorganic/Organic Hybrid Functionalized Materials, College of Chemistry
Chemical Engineering, Anhui University, Hefei 230601, China.
&
E-mail addresses: lilei@ahu.edu.cn (L. Li), xuanjun@ahu.edu.cn (J. Xuan).
https://doi.org/10.1016/j.cclet.2021.03.010
1001-8417/© 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
Please cite this article as: S. Zhou, B. Cai, C. Hu et al., Visible light and base promoted O-H insertion/cyclization of para-quinone methides with
aryl diazoacetates: An approach to 2,3-dihydrobenzofuran derivatives, Chin. Chem. Lett., https://doi.org/10.1016/j.cclet.2021.03.010

G Model
CCLET-6206; No. of Pages 5
S. Zhou, B. Cai, C. Hu et al.
Chinese Chemical Letters xxx (xxxx) xxx–xxx
Fig. 1. Bioactive compounds containing 2,3-dihydrobenzofuran moiety.
[15], cyclopropanation [16], rearrangement reaction [17] and
others [18]. Regarding to X-H insertion reactions [15], to the best of
our knowledge, the reported photochemical process mainly
limited to one-step carbene insertion to construct single C–N,
C–O or C–Si bond (Scheme 1a).
Within the frame of our ongoing research interests in visible-
light-induced chemical transformations [19] and [4
+ m]
cycloaddition reaction of p-QMs [4l,4m], we envisage that ortho-
hydroxyphenyl-substituted p-QMs 1 might be suitable carbene
trapping reagents because of the suitable pKA of phenol and easy
formation of hydrogen bond between phenols and aryl diazo-
acetates [15d,15f]. As shown in Scheme 1b, upon visible light
irradiation, A would be formed through insertion reaction of
photogenerated carbene species into OꢀꢀH bonds of 1. Then, an
intramolecular cyclization of A might occur with the assistance of
an appropriate base. This expected one-pot two step annulation
process could provide a green and efficient method to access 2,3-
dihydrobenzofurans 3. Herein, we would like to describe our
preliminary investigations on this study.
To test the feasibility of our design, we started our investigation
with the reaction of ortho-hydroxyphenyl-substituted p-QM 1a and
methyl 2-diazo-2-phenylacetate 2a as model substrates (Scheme
2). It is well known that diazo compounds can serve as 1,10-dipolar
C1 synthons in various cycloaddition processes. However, the
desired 2,3-dihydrobenzofuran 3aa could not be obtained by direct
reacting of 1a and 2a in the presence of Cs2CO3 as base at room
temperature or 50 ꢁC which might due to the steric effect (Scheme
Scheme 2. Initial investigation.
2a). In contrast, treatment of 1a and 2a in 1,4-dioxane under the
irradiation of 24 W blue LEDs for 12 h, followed by addition of
Cs2CO3 lead to the formation of 3aa in 73% yield over two steps with
1.2:1 diastereoselectivity (Scheme 2b). Note that, the two diaster-
eomers of 3aa were unambiguously confirmed by X-ray diffraction
analysis (CCDC: 2039981 and CCDC: 2039982). For detailed
condition optimizations, please see Supporting information.
Next, we turned our attention to investigate the substates scope
of this visible light and base promoted 2,3-dihydrobenzofuran
formation process (Scheme 3). Regarding to ortho-hydroxyphenyl-
substituted p-QMs components, both electron-donating groups
(e.g., -Me) and electron-withdrawing groups (e.g., -F, -Cl, -Br, -NO2)
can be successfully introduced to aryl ring of 1, affording the
corresponding heterocycles 3aa-ga in good yields with moderate
diastereoselectivities. Only one-step OꢀꢀH insertion product was
isolated in 10% yield when methoxy substituted p-QM 1c was
involved. It was reported that hydrogen-bonding interaction
between the proton of phenols and carbonyl group of aryl
diazoacetates played an important role for OꢀꢀH insertion reaction
[15d,15f]. The pKa value of para-methoxy phenol (10.21) showed
that this type of substrate had weaker acidic activity and low
reaction efficiency for OꢀꢀH insertion. Moreover, a wide range of
substations on the different positions of phenyl ring of the diazo
compounds could be well tolerated, yielding the dihydrobenzo-
furans 3abꢀ3ag in synthetically useful to high yields with
moderate dr. To our delight, 3ad still could be isolated in 71%
yield when expand the reaction to 0.5 mmol scale. It was
noteworthy that disubstituted aryl diazoacetate 2h was also
amenable substrate to give product 3ah in 73% yield with 1.2:1 dr.
Then, substituent modification of ester group in diazo compounds
was investigated. Replacement of methyl group in 2a with other
primary alkyl groups (3ai-ak, 3ao, 3ap), secondary alkyl group
(3al), cyclic alkyl groups (3am and 3an) were all proved to be
successful, providing the corresponding heterocycles in acceptable
results (42%–73% yields, 1:1ꢀ2.3:1 dr). It should be pointed out
that carbene cyclopropanation or cyclopropenation products were
not observed in the cases of substrates containing unsaturated
Scheme 1. 2,3-Dihydrobenzofuran synthesis via one-pot visible light-promoted O-
H insertion/cyclization cascade.
2

G Model
CCLET-6206; No. of Pages 5
S. Zhou, B. Cai, C. Hu et al.
Chinese Chemical Letters xxx (xxxx) xxx–xxx
Scheme 3. Reaction scopes. Reaction condition: 1 (0.4 mmol), 2 (0.1 mmol), Cs2CO3 (0.4 mmol), in 1,4-dioxane (2.0 mL), irradiation by 24 W blue LEDs at room temperature.
a
b
Isolated yield. Reaction was conducted with 0.5 mmol scale. Sodium bis(trimethylsilyl)amide (0.4 mmol) was used as base.
double or triple bonds. Some commonly used simple diazo
compounds, such as ethyl diazoacetate and 3-diazopentane-2,4-
dione are not suitable for this transformation. More significantly,
the synthetic potential of the method could be further highlighted
by successfully introducing some useful molecules, such citronel-
lol, cholesterol, oleyl alcohol and
L-menthol, into the final
heterocycles (3aq-3at). It was found that tert-Bu group in
p-QMs 1 had significant effect on the reaction efficiency. Only
one-step OꢀꢀH insertion product can be obtained when the two
tert-Bu groups were replaced by i-Pr groups.
To furtherdemonstrate the syntheticutilityof thisreaction, some
follow-up chemistry was performed (Scheme 4). Treatment of one
single isomer of 3aa with LiAlH4 in THF provided the reductive
product 5 in 89% yield. In addition, a decarboxylative aromatization
of 3aa in NaOH/MeOH under reflux conditions afforded 2,3-diaryl
substituted benzofuran 6 in 53% isolated yield. Note that, further
functionalization of C-Br bond in final product 3fa was succeed by
using employing palladium catalyzed Suzuki cross-coupling and
Sonogashira cross-coupling as examples, affording the correspond-
ing products 6 and 7 with 86% and 82% yield, respectively.
Scheme 4. Synthetic transformations.
3

G Model
CCLET-6206; No. of Pages 5
S. Zhou, B. Cai, C. Hu et al.
Chinese Chemical Letters xxx (xxxx) xxx–xxx
Appendix A. Supplementary data
Supplementarymaterialrelatedtothisarticlecanbefound, inthe
online version, at doi:https://doi.org/10.1016/j.cclet.2021.03.010.
References
[1] (a) R.S. Ward, Chem. Soc. Rev. 11 (1982) 75–125:
(b) D.C. Chauret, C.B. Bernard, J.T. Arnason, et al., J. Nat. Prod. 59 (1996)
152–155:
(c) R.S. Ward, Nat. Prod. Rep. 16 (1999) 75–96:
(d) N. Beldjoudi, L. Mambu, M. Labaïed, et al., J. Nat. Prod. 66 (2003) 1447–
1450:
(e) T. She, X.N. Wang, H.X. Lou, Nat. Prod. Rep. 26 (2009) 916–935:
(f) A. Radadiya, A. Shah, Eur. J. Med. Chem. 97 (2015) 356–376:
(g) R.J. Nevagi, S.N. Dighe, S.N. Dighe, Eur. J. Med. Chem. 97 (2015) 561–581.
[2] (a) A. Goel, A. Kumar, A. Raghuvanshi, Chem. Rev. 113 (2013) 1614–1640:
(b) H.Q. Yin, B.W. Lee, Y.C. Kim, D.H. Sohn, B.H. Lee, Arch. Pharm. Res. 27 (2004)
919–922.
[3] (a) T.D. Sheppard, J. Chem. Res. 35 (2011) 377–385:
(b) C. Zhu, Y. Ding, L.W. Ye, Org. Biomol. Chem. 13 (2015) 2530–2536:
(c) J.R. Chen, X.Q. Hu, L.Q. Lu, W.J. Xiao, Chem. Rev. 115 (2015) 5301–5365:
(d) B.M. Trost, O.R. Thiel, H.C. Tsui, J. Am. Chem. Soc. 125 (2013) 13155–13164:
(e) E.D. Coy B, L. Jovanovic, M. Sefkow, Org. Lett. 12 (2010) 1976–1979:
(f) J. Meng, T. Jiang, H.A. Bhatti, et al., Org. Biomol. Chem. 8 (2010) 107–113:
(g) D.H. Wang, J.Q. Yu, J. Am. Chem. Soc. 133 (2011) 5767–5769:
(h) X.X. Sun, H.H. Zhang, G.H. Li, L. Meng, F. Shi, Chem. Commun. 52 (2016)
2968–2971:
(i) Y. Cheng, Z. Gang, W. Li, P. Li, Org. Chem. Front. 5 (2018) 2728–2733:
(j) T. Zhou, T. Xia, Z. Liu, L. Liu, J. Zhang, Adv. Synth. Catal. 360 (2018) 4475–
4479.
[4] (a) J.Y. Wang, W.J. Hao, S.J. Tu, B. Jiang, Org. Chem. Front. 7 (2020) 1743–1778:
(b) C.G.S. Lima, F.P. Pauli, D.C.S. Costa, et al., Eur. J. Org. Chem. 2020 (2020)
2650–2692:
(c) L. Caruana, M. Fochi, L. Bernardi, Molecules 20 (2015) 11733–11764:
(d) K.Zhao Y. Zhi, T. Shu, et al., Angew. Chem. Int. Ed. 55 (2016) 12104–12108:
(e) A. Parra, M. Tortosa, ChemCatChem 7 (2015) 1524–1526:
(f) P. Chauhan, U. Kaya, D. Enders, Adv. Synth. Catal. 359 (2017) 888–912:
(g) W. Li, X. Xu, P. Zhang, P. Li, Chem. Asian J. 13 (2018) 2350–2359:
(h) Y.J. Xiong, S.Q. Shi, W.J. Hao, S.J. Tu, B. Jiang, Org. Chem. Front. 5 (2018)
3483–3487:
(i) S. Liu, X.C. Lan, K. Chen, et al., Org. Lett. 19 (2017) 3831–3834:
(j) W. Li, H. Yuan, Z. Liu, et al., Adv. Synth. Catal. 360 (2018) 2460–2464:
(k) Q. Liu, S. Li, X.Y. Chen, K. Rissanen, D. Enders, Org. Lett. 20 (2018) 3622–
3626:
(l) F. Jiang, F.R. Yuan, L.W. Jin, G.J. Mei, F. Shi, ACS Catal. 8 (2018) 10234–10240:
(m) X.L. Jiang, S.F. Wu, J.R. Wang, G.J. Mei, F. Shi, Adv. Synth. Catal. 360 (2018)
4225–4235:
(n) J.R. Wang, X.L. Jiang, Q.Q. Hang, et al., J. Org. Chem. 84 (2019) 7829–7839:
(o) Y.C. Cheng, C.S. Wang, T.Z. Li, et al., Org. Biomol. Chem. 17 (2019) 6662–
6679:
Scheme 5. Mechanism studies.
To betterunderstandingofthereactionmechanism,somecontrol
experiments were subsequently conducted. As shown in Scheme 5,
treatment of 1a and 2a under standard reaction conditions for 12 h
gavetheone-stepO-Hinsertionproduct8in81%isolatedyield.Note
that, visible light irradiation was crucial for the formation of 8
(Scheme 5a). 8 could transfer to final 2,3-dihydrobenzofuran 3aa in
87% yield by treating themwith Cs2CO3 in 1,4-dioxane (Scheme 5b).
Based on above experiment results and literature reports, a
plausible reaction mechanism was proposed in Scheme 5c. Initially,
upon irradiation of aryl diazoacetatewith blue LED generated carbene
species with the release of molecule nitrogen [14]. Then, insertion of
carbene species into OꢀꢀH bond of 1a afforded product 8 [15]. Under
basic reaction conditions, deprotonation of 8 gave carbon anion
intermediate 9, which subsequently cyclized to produce 10. Finally,
protonation of 10 delivered final 2,3-dihydrobenzofuran 3aa.
In summary, we have developed a visible light and base
promoted O-H insertion/cyclization of para-quinone methides
with aryl diazoacetates. By using the strategy, a wide range of 2,3-
dihydrobenzofuran derivatives can be obtained in good yields and
moderate diastereoselectivities. More significantly, the successful
introduction of some useful complex structures into the 2,3-
dihydrobenzofuran heterocycles and synthetic transformation of
the final products further renders this approach attractive and
valuable. The further discovery of new visible light-promoted
carbene transfer reactions is currently underway in our laboratory.
(p) M. Sun, C. Ma, S.J. Zhou, et al., Angew. Chem. Int. Ed. 58 (2019) 8703–8708:
(q) S. Zhang, X. Yu, J. Pan, et al., Org. Chem. Front. 6 (2019) 3799–3803:
(r) Z. Li, W. Wang, H. Jian, et al., Chin. Chem. Lett. 30 (2019) 386–388:
(s) X. Cheng, S.J. Zhou, G.Y. Xu, et al., Adv. Synth. Catal. 362 (2020) 523–527:
(t) S.J. Zhou, X. Cheng, C.X. Hu, et al., Sci. China Chem. 64 (2021) 61–65:
(u) J.P. Tan, H. Zhang, Z. Jiang, et al., Adv. Synth. Catal. 362 (2020) 1058–1063:
(v) S.F. Wu, M.S. Tu, Q.Q. Hang, et al., Org. Biomol. Chem. 18 (2020) 5388–5399.
[5] X.M. Chen, K.X. Xie, D.F. Yue, et al., Tetrahedron 74 (2018) 600–605.
[6] Y. Zhi, K. Zhao, C.V. Essen, K. Rissanen, D. Enders, Org. Chem. Front. 5 (2018)
1348–1351.
[7] L. Liu, Z. Yuan, R. Pan, et al., Org. Chem. Front. 5 (2018) 623–628.
[8] (a) J. Zhou, G. Liang, X. Hu, L. Zhou, H. Zhou, Tetrahedron 74 (2018) 1492–1496:
(b) J.P. Tan, P. Yu, J.H. Wu, et al., Org. Lett. 21 (2019) 7298–7302:
(c) G. Singh, S. Kumar, A. Chowdhury, R.V. Anand, J. Org. Chem. 84 (2019)
15978–15989:
(d) H. Lu, H.X. Zhang, C.Y. Tan, J. Org. Chem. 84 (2019) 10292–10305.
[9] K. Zielke, O. Kovác9, M. Winter, J. Pospíšil, M. Waser, Chem. Eur. J. 25 (2019)
8163–8168.
[10] (a) J.M.R. Narayanam, C.R.J. Stephenson, Chem. Soc. Rev. 4 (2011) 102–113:
(b) Y. Xi, H. Yi, A. Lei, Org. Biomol. Chem. 11 (2013) 2387–2403:
(c) C.K. Prier, D.A. Rankic, D.W.C. MacMillan, Chem. Rev.113 (2013) 5322–5363:
(d) M.N. Hopkinson, B. Sahoo, J.L. Li, F. Glorius, Chem. Eur. J. 20 (2014) 3874–
3886:
Declaration of competing interest
The authors report no declarations of interest.
Acknowledgments
(e) N.A. Romero, D.A. Nicewicz, Chem. Rev. 116 (2016) 10075–10166:
(f) L. Marzo, S. Pagire, O. Reiser, B. König, Angew. Chem. Int. Ed. 57 (2018)
10034–10072:
(g) Y.Z. Cheng, X. Zhang, S.L. You, Sci. Bull. 63 (2018) 809–811:
(h) L. Lu, J.L. Zhang, Chin. J. Org. Chem. 39 (2019) 3308–3309:
(i) B.G. Cai, J. Xuan, W.J. Xiao, Sci. Bull. 64 (2019) 337–350:
(j) Y. Chen, L.Q. Lu, D.G. Yu, C.J. Zhu, W.J. Xiao, Sci. China Chem. 62 (2019) 24–57:
(k) T.Y. Shang, L.H. Lu, Z. Cao, et al., Chem. Commun. 55 (2019) 5408–5419:
(l) X.Y. Yu, Q.Q. Zhao, J. Chen, W.J. Xiao, J.R. Chen, Acc. Chem. Res. 53 (2020)
1066–1083:
We are grateful to the National Natural Science Foundation of
China (Nos. 21971001, 21702001), and the Start-up Grant from
Anhui University for financial support of this work.
4

G Model
CCLET-6206; No. of Pages 5
S. Zhou, B. Cai, C. Hu et al.
Chinese Chemical Letters xxx (xxxx) xxx–xxx
(m) J. Xuan, X.K. He, W.J. Xiao, Chem. Soc. Rev. 49 (2020) 2546–2556:
(n) W. Xiao, J. Wu, Chin. Chem. Lett. 31 (2020) 3083–3094:
(o) H.G. Zhang, H. Chen, C. Zhu, S. Yu, Sci. China Chem. 63 (2020) 637–647:
(p) X. Lv, H. Xu, Y. Yin, X. Zhao, Z. Jiang, Chin. J. Chem. 38 (2020) 1480–1488:
(q) K. Sun, Q.Y. Lv, X.L. Chen, et al., Green Chem. 23 (2021) 232–248.
[11] I. Jurberg, H.M.L. Davies, Chem. Sci. 9 (2018) 5112–5118.
[12] T. Xiao, M. Mei, Y. He, L. Zhou, Chem. Commun. 54 (2018) 8865–8868.
[13] (a) H.M.L. Davies, J.R. Manning, Nature 451 (2008) 417–424:
(b) M.P. Doyle, R. Duffy, M. Ratnikov, Z. Zhou, Chem. Rev. 110 (2010) 704–724(c)
X. Guo, W. Hu, Acc. Chem. Res. 46 (2013) 2427–2440(d) S.F. Zhu, Q.L. Zhou, Sci.
Rev. 1 (2014) 580–603:
(e) H.J. Knöker, I. Bauer, Chem. Rev. 115 (2015) 3170–3387:
(f) L. Mertens, R.M. Koenigs, Org. Biomol. Chem. 14 (2016) 10547–10556:
(g) Y. Xia, D. Qiu, J. Wang, Chem. Rev. 117 (2017) 13810–13889.
[14] (a) L.W. Ciszewski, K. Rybicka-Jasinska, D. Gryko, Org. Biomol. Chem. 17 (2019)
432–448:
[16] (a) Y. Guo, T.V. Nguyen, R.M. Koenigs, Org. Lett. 21 (2019) 8814–8818:
(b) F. He, R.M. Koenigs, Chem. Commun. 55 (2019) 4881–4884:
(c) X. Zhang, C. Du, H. Zhang, et al., Synthesis 51 (2019) 889–898:
(d) R. Hommelsheim, Y. Guo, Z. Yang, C. Empel, R.M. Koenigs, Angew. Chem. Int.
Ed. 58 (2019) 1203–1207.
[17] (a) J. Yang, J. Wang, H. Huang, et al., Org. Lett. 21 (2019) 2654–2657:
(b) Z. Yang, Y. Guo, R.M. Koenigs, Chem. Eur. J. 25 (2019) 6703–6706:
(c) K. Orłowska, K. Rybicka-Jasin’ska, P. Krajewski, D. Gryko, Org. Lett. 22
(2020) 1018–1021.
[18] (a) Y. Wei, S. Liu, M.M. Li, et al., J. Am. Chem. Soc. 141 (2019) 133–137:
(b) S. Jana, Z. Yang, C. Pei, X. Xu, R.M. Koenigs, Chem. Sci. 10 (2019) 10129–
10134:
(c) Q.L. Zhang, Q. Xiong, et al., Angew. Chem. Int. Ed. 59 (2020) 14096–14100:
(d) A.F. da Silva, M.A.S. Afonso, R.A. Cormanich, I.D. Jurberg, Chem. Eur. J. 26
(2020) 5648–5653:
(e) R. Cheng, C. Qi, L. Wang, et al., Green Chem. 22 (2020) 4890–4895:
(f) M.A. Ansari, D. Yadav, M.S. Singh, Chem. Eur. J. 26 (2020) 8083–8089.
[19] (a) J. Xuan, A. Studer, Chem. Soc. Rev. 46 (2017) 4329–4346:
(b) B.G. Cai, Z.L. Chen, G.Y. Xu, J. Xuan, W.J. Xiao, Org. Lett. 21 (2019) 4234–
4238:
(b) T.B. Hua, Q.Q. Yang, Y.Q. Zou, Molecules 24 (2019) 3191:
(c) Z. Yang, M.L. Stivanin, I.D. Jurberg, R.M. Koenigs, Chem. Soc. Rev. 49 (2020)
6833–6847:
(d) S. Jana, Y. Guo, R.M. Koenigs, Chem. Eur. J. 27 (2021) 1270–1281.
[15] (a) C. Empel, F.W. Patureau, R.M. Koenigs, J. Org. Chem. 84 (2019) 11316–11322:
(b) M.L. Stivanin, A.A.G. Fernandes, A.F. da Silva, C.Y. Okada Jr, I.D. Jurberg, Adv.
Synth. Catal. 362 (2020) 1106–1111:
(c) Q.Q. Ge, J.S. Qian, J. Xuan, J. Org. Chem. 84 (2019) 8691–8701:
(d) X.K. He, B.G. Cai, Q.Q. Yang, L. Wang, J. Xuan, Chem. Asian J. 14 (2019) 3269–
3273:
(c) S. Jana, Z. Yang, F. Li, et al., Angew. Chem. Int. Ed. 59 (2020) 5562–5566:
(d) F. He, F. Li, R.M. Koenigs, J. Org. Chem. 85 (2020) 1240–1246:
(e) C. Empel, S.J. Orcid, C. Pei, T.V. Nguyen, R.M. Koenigs, Org. Lett. 22 (2020)
7225–7229:
(e) J. Lu, X.K. He, X. Cheng, et al., Adv. Synth. Catal. 362 (2020) 2178–2182:
(f) X.K. He, J. Lu, A.J. Zhang, et al., Org. Lett. 22 (2020) 5984–5989:
(g) B.G. Cai, S.S. Luo, L. Li, et al., CCS Chem. 2 (2020) 2764–2771:
(h) C. Ye, B.G. Cai, J. Lu, et al., J. Org. Chem. 86 (2021) 1012–1022.
(f) J. Chen, S. Liu, X. Lv, et al., J. Org. Chem. 85 (2020) 13920–13928:
(g) J. Yang, G. Wang, S. Chen, et al., Org. Biomol. Chem. 18 (2020) 9494–9498.
5